Glucagon-like peptide-1 (GLP-1) induces numerous biological effects such as stimulating insulin secretion, inhibiting glucagon secretion, inhibiting gastric emptying, inhibiting gastric motility or intestinal motility, enhancing glucose utilization, and inducing weight loss. GLP-1 may further act to prevent the pancreatic β-cell deterioration that occurs as non-insulin dependent diabetes mellitus (NIDDM) progresses. A significant characteristic of GLP-1 is its ability to stimulate insulin secretion without the associated risk of hypoglycemia that is seen when using insulin therapy or some types of oral therapies that act by increasing insulin expression.
The usefulness of therapy involving GLP-1 peptides has been limited by the fact that GLP-1(1-37) is poorly active, and the two naturally occurring truncated peptides, GLP-1(7-37)OH and GLP-1(7-36)NH2, are rapidly cleared in vivo and have extremely short in vivo half lives. It is known that endogenously produced dipeptidyl-peptidase IV (DPP-IV) inactivates circulating GLP-1 peptides by removing the N-terminal histidine and alanine residues and is a major reason for the short in vivo half-life.
Various approaches have been undertaken to extend the elimination half-life of a GLP-1 peptide or reduce clearance of the peptide from the body while maintaining a biological activity. U.S. Pat. No. 5,705,483 teaches GLP-1 peptide analogs made resistant to DPP-IV degradation by the incorporation of modifications at the N-terminus of the peptide. An alternative approach for extending the half-life of GLP-1 peptides is derivatization, wherein large acyl groups that prevent DPP-IV from accessing the N-terminus of the peptide are attached to various amino acids of GLP-1 (See International Application No. PCT/DK97/00340, filed Aug. 22, 1997 entitled “GLP-1 Derivatives,” which claims the benefit of DK Provisional Application Nos. 0931/96 filed Aug. 30, 1996, 1259/96 filed Nov. 8, 1996 and 1470/96 filed Dec. 20, 1996).
Particular GLP-1 analogs are described in U.S. patent application Ser. No. 60/346,474 filed Jan. 8, 2002, and U.S. patent application Ser. No, 60/405,097 filed Aug. 21, 2002, now International Application No. PCT/US03/058203, filed Jan. 3, 2003, all entitled “Extended Glucagon-Like Peptide-1 Analogs” and are incorporated herein in their entirety. These applications describe analogs of GLP-1(7-37)OH wherein various amino acids, when added to the C-terminus, yield GLP-1 peptide analogs with an extended half-life and reduced clearance than that of the native molecule. Furthermore, GLP-1 logs with increased potency are described in U.S. patent application Seri. No. 60/314,573 filed Aug. 23, 2001, now International Application No. PCT/US02/21325, filed Aug. 14, 2002, entitled “Glucagon-Like Peptide-1 Analogs” (incorporated herein). Exendin-4 can act at the GLP-1 receptor in vitro on certain cell types including insulin-secreting cells. [Goke, et al., J. Biol. Chem., (1993)268:19650-19655]. Particular PEGylated exendin and exendin agonist molecules are described in International Application Number PCT/US00/11814 (incorporated herein in its entirety).
While various approaches have resulted in GLP-1 compounds with a longer half-life or greater potency than that of native GLP-1, additional approaches that could be used either alone or in combination with known approaches are needed to further decrease GLP-1 compound clearance and increase GLP-1 compound half-life thereby optimizing its ability to be useful as a therapeutic that can be administered a minimum number of times during a prolonged period of time. Covalent attachment of one or more molecules of polyethylene glycol to a small, biologically active peptide such as GLP-1 or exendin-4 poses the risk of introducing adverse characteristics such as instability to the molecule and reduction in bioactivity so severe as to make the molecule unsuitable for use as a therapeutic. The present invention; however, is based on the finding that covalent attachment of one or more molecules of PEG to particular residues of a GLP-1 compound results in a biologically active, PEGylated GLP-1 compound with an extended half-life and reduced clearance when compared to that of native GLP-1 or Val8-GLP-1 (or native exendin-4 for modified exendin-4 peptides of the invention).
The PEGylated GLP-1 compounds of the invention have greater usefulness as a therapeutic as well as greater convenience of use than native GLP-1 because they retain all or a portion of a biological activity of native GLP-1 yet have an enhanced half-life and/or reduced clearance when compared to that of the native GLP-1 compound or to that of Val8-GLP-1(7-37)OH. GLP-1(7-37) has a serum half-life of only 3 to 5 minutes. GLP-1(7-36) amide has a time action of about 50 minutes when administered subcutaneously. Even GLP-1 analogs and derivatives that are resistant to endogenous protease cleavage, do not have half-lives long enough to avoid repeated administrations over a 24 hour period. PEGylated GLP-1 compounds of the invention may have a half-life in excess of 24 hours allowing for fewer administrations of the PEGylated GLP-1 compound while maintaining a high blood level of the compound over a prolonged period of time. Such PEGylated GLP-1 compounds may be used therapeutically to treat subjects with disorders including, but not limited to, diabetes, obesity, gastric and/or intestinal motility abnormalities, and gastric and/or intestinal emptying abnormalities with a particular advantage being that the PEGylated GLP-1 compounds of the invention require fewer doses during a 24 hour period, increasing both the convenience to a subject in need of such therapy and the likelihood of subject's compliance with dosing requirements.